This invention relates to electrochemical microsensors and particularly to structures or packages which may be advantageously utilized for the manufacture of a wide variety of miniature or “micro” sensors. This invention also relates to methods for the manufacture of such microsensors and packages therefor. Electrochemical microsensors have a wide range of existing and potential uses in various arts for chemical detection and measurement, especially in biochemical applications such as in medicine. In order to succeed in the point of care market, the biosensor systems must meet their application needs. Planar electrochemical sensors with microelectronic production techniques are known as an elegant approach to meet these requirements. Due to the batch processing and high precision of microelectronic techniques, the miniaturized planar sensors have major advantages including small dimension, low cost per sensor, high reproducibility and the possibility of smart sensor realizations.
In the past few years, a number of micro-fabricated sensors have been designed and developed by microelectronic techniques as exemplified in U.S. Pat. No. 4,874,500. These sensors are usually fabricated by opening wells in a silicon chip using IC technologies and filling the wells with sensing chemicals. The bottoms of the wells are typically coated with silver and the surface of the silver converted to silver chloride. Then a hydrogel containing a known concentration of chloride ions is placed into the well on top of the silver chloride, creating a known electrochemical potential between the hydrogel and the silver chloride electrode. The well is then covered with a membrane that has in it chemical that effects the attraction of the target ion. An electrochemical potential is developed between the silver and the unknown liquid through the hydrogel that depends on the relative concentration of the target ion between the membrane and the target liquid, which is determined by the concentration of the target ion in the target liquid. The are usable for detecting various ions as well as gases. However, in these cases, silicon is only a substrate and does not play any role in the sensing mechanism itself. Using silicon to make the wells is expensive. Multiple sensors on the same chip are incompatible requiring wide separation which in turn, causes low yields and large chip sizes. Low yields and large chip sizes combined with expensive fabrication processes causes the finished product to be costly. Our alternative avoids these problems and also uses inexpensive materials and processes for an order of magnitude cost advantage. There also exist some problems concerning the final package of the sensors because a chemical sensor on an insulating substrate is almost always easier to package than on a piece of silicon with conductive edges in need of insulation. Moreover, many chemical sensor materials are incompatible with IC processing; therefore the very point of using silicon is forfeit for many chemical sensors.
For connection with associated electronics, such micro-fabricated sensors have relied upon a conductor extending from the sensor well that is on the same surface as the opening in the sensor well. Placing such pins so they made good electrical contact while at the same time not damaging the sensor is difficult. Alternatively, wire bonding is used to make electrical connection to the conductor on the sensor. The completed assembly is delicate and easily broken. Also, since the hydrogel in the microsensors are vulnerable to elevated temperatures, soldered connections are not a viable option. A more robust construction would be to bring the electrode connection out of the sensor well to the side of the sensor opposite from the opening in the sensor well itself. Such a construction is difficult to achieve using silicon fabrication techniques.
Pressure type electrical contact buttons are described in U.S. Pat. Nos. 5,364,277, 5,197,184 and 5,207,887 which are formed integrally with an electrical trace fixed on a substrate and which project through and outwardly of the substrate for make contact by pressing against another contact element. However, these contacts are for employment as terminal connections for wire cable terminations and there is no suggestion that these contacts could have any utility for electrochemical microsensors or how they might be adapted to be employed therewith. Lately, flexible polyimide film (Kapton) has been used as a substrate in microfabricated planar sensor arrays. Photolithography and sputtering technologies are used in the fabrication of the sensor arrays. These sensor arrays have shown good analytical properties for in-vivo measurements and have solved the problems with respect to membrane optimization, adhesion of membrane to its substrate, etc., but the sputtering process causes the fabrication of sensors to be expensive and time consuming